The embodiments described herein relate generally to an x-ray diffraction imaging (XDI) system and, more particularly, to an angle-dependent XDI system.
Known security detection systems are used at travel checkpoints to inspect carry-on and/or checked bags for concealed weapons, narcotics, and/or explosives. At least some known security detection systems include x-ray imaging systems. In an x-ray imaging system, an x-ray source transmits x-rays through an object or a container, such as a suitcase, towards a detector, and the detector output is processed to identify one or more objects and/or one or more materials in the container.
At least some known security detection systems include an XDI system, e.g., a multi-detector inverse fan beam (MIFB) XDI system that uses an inverse fan-beam geometry (a large source and a small detector) and a multi-focus x-ray source (MFXS). At least some known XDI systems provide an improved discrimination of materials, as compared to that provided by other known x-ray imaging systems, by measuring d-spacings between lattice planes of micro-crystals in materials. Further, x-ray diffraction may yield data from a molecular interference function that may be used to identify other materials, such as liquids, in a container.
Known MIFB XDI systems feature an x-ray multisource emitting a multiplicity of x-ray beams, such that each object voxel is irradiated from several different directions, and such that these systems measure spatially-resolved x-ray diffraction profiles of the constituent voxels of inhomogeneous, extended objects. However, currently, all photons belonging to the same object voxel are merely summed to yield an average XDI profile. This average XDI profile has a fourfold dimensionality, i.e., three spatial dimensions defining the voxel location, and one momentum dimension. As such, no provisions are currently made for separately storing angle dimensional information about the measured photons. Such angle dimensional information relates to the direction at which a primary beam irradiates a certain object voxel relative to a system axis. Therefore, since the angle is assumed to be isotropic, no use is currently made in the threat/no threat classification procedure of possible differences in the form of XDI profiles acquired from different irradiation directions for the same voxel.
For liquid, amorphous and micro-crystalline powder samples there is no preferred orientation direction and the XDI profile is independent of irradiation angle. Voxels however containing an appreciable amount of single-crystal material have a statistically-varying preferred orientation direction, and the XDI profile changes according to the relative angles of the primary x-ray beam to this orientation direction and according to the number of crystallites included in a voxel signal. One example of substances whose XDI profiles vary with angle is the class of anisotropic substances, including coarse-grain powders. Since such anisotropic substances have a relatively high degree of single crystal material compared to isotropic substances such as fine powders. Not leveraging use of this anisotropic nature may lead to less than optimum detection performance.